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I would also be concerned that the force would be different based on the type of filament used, maybe even down to the supplier. Printer settings such as heat and speed and how much underextrusion would also affect the spring force. Since this is a fix to avoid underextrusion I think that is too big of a risk requiring a really consistent print quality for a part like this.

It is my understanding that the replicator 5th gen series has this, or will have this once it is released. I have not seen enough detail to know how theirs attaches. Maybe some insight can be gleaned from that design?

Robert, I read this post you made in the thread about UM2 extruder pulling force:
I don't have a 3d printer, I am planning on getting the UM2, with my only concern being these underextrusion issues (which I know may be hotend related).
If the UM1 design was so superior, why don't UM2 owners work on a way to make that design work on the UM2? I know I am speaking from a point of ignorance.
I suspect two things would change.
1) the current supplied by the controller is probably different.
Couldn't that be fixed with an inline microcontroller (and maybe even simpler circuitry?)
2) the extrusion distance per step is probably different.
Isn't this just a software setting somewhere? Something like extrusion distance per step?
It just seems to me like there was an existing solution at some point that got thrown out.
Again, my apologies for any ignorance I am showing about the software, electronics, and physical function of these extruders. I understand the UM2 one pretty well, but know VERY little about the UM1 one, partly because I think most users modified it from the original stock.

OOOOH! Printable 3d bar graphs!
I can see it now!
"It looks like company XY has shown improvement over last week"
"No, that is just because it is in the corner, sorry we had some issues keeping it on the bed"

Couldn't you also flip it over like GR5 suggests and turn on support? Cura should support the back then, and if you rough up the inside by scraping out support that should not be such a big deal.
I would think cleaning out support would end up being better than the unknown of dealing with the bulk of the print being printed on a fairly long bridge.
I speak from only ignorance and watching videos and reading though. I am still 3d printerless as I wait for the tax monies.

Love the idea of those extruders, but I imagine they are quite heavy. The main bonus for bowden feeding like on both ultimakers is to reduce the weight of the print head.
I would be concerned going with a printer specifically engineered to have a lightweight print head.
I would suspect a design with a sliding bed where the bed handles two axis would be best for a heavy head like this.
On the other hand, I think that the clay extrusion is meant to be done at pretty low speeds where the extra mass might not be an issue.

I know the intent here is to use stock parts and to make the fix fully printable, but in the thread in this folder regarding flexible filament, there is a link to what appears to me to be a much better knurled bolt/knob/thingy.
http://www.ebay.at/itm/281102410932?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
I don't know if the radii match, but the design is great, with the notches fully perpendicular to the direction of motion and the shape keeping the filament in place.

I really like the look of this. I can't easily tell, but it looks like the opening below the drive wheel is quite open so that any flecks of filament produced can easily fall out the bottom. Along with your bearing upgrade to the feed wheel you might be on to something here.

There are some good design elements here. I really like the idea of a place for the filament bits to exit.
I disagree with the piece on the right side though. The point of the part that pushes the filament against the knurled head is to provide as little friction as possible in the linear direction of the filament feed.
This design has two contact points where the current UM2 has one contact point. This design also has static contact points that will provide much more friction than the wheel in the original UM2.
Finally, both this design and the movie reel one you showed apply offset pressure to the filament. Over time (users who leave filament in the machine while not in use) a static filament will bend/warp in this design which will then cause issues when this curved portion exits the extruder housing or along the path of the bowden tube. It would take only a very small kink in the shape of the filament to cause friction in the bowden tube which is already VERY tight if you are nearing 3mm filament thickness.
I think this basic design is still very valid, it is nice and simple, but I think that the contact point that puts pressure on the drive bolt has to be exactly opposite the contact point to avoid any tendency to bend, and that contact point should be as much of a low friction point as possible.
I definitely agree that the diamond design of the knurled metal piece is sub optimal.
Another idea to improve contact along the filament would be to increase the diameter of the knurled knob/bolt/whatever. This is not a simple change as that would change torques and the linear travel distance of a step (which would require software changes of some type).
Very cool to see this open discussion!

Thanks for the response!
Been pulled away with semi-work related stuff lately, I was hoping for some kind of official statement from the ultimaker folks that third party purchases of new hardware is supported.
I understand that this is probably the wrong place to ask.
I will wait till we have the money (stupid slow taxes) and then either call or email their support directly. Figured if it was answered in the forums then it might help others and make them feel more warm and fuzzy about buying through re-distributors.

I am new to 3d modeling, and have some 3d models I really want to break apart, add connections, etc...
Is there any free tools that are good at this sort of thing?
Right now I am looking at blender and meshmixer. I like 123d Design for making new mechanical parts, but it does not see to do that well for taking existing models apart.
Also, maybe I have not searched for the right things yet, but it seems really hard to handle assemblies in blender. I feel like there should be a way to make custom snap-to points so I can take objects apart, fiddle, and then snap them perfectly back together. I can break them apart in blender, but then fitting them perfectly back together as separate objects seems super fiddly, especially when I want to design linkages for them, etc... Maybe it is just the wrong tool for the job.

Totally amazing!
More than anything, for some reason the stuff I am most excited about making with my 3d printer are cool models with built in lighting, custom stands, etc...
This is right up my alley!